Ion implanters have been used for treating silicon wafers by bombardment of the wafers with a beam. The ion beam dopes the wafers with impurities of controlled concentration to yield a semiconductor wafer that in turn is used to fabricate an integrated circuit. One important factor in such implanters is the throughput or number of wafers that can be treated in a given time.
High current ion implanters include a spinning disk support for moving multiple silicon wafers through the ion beam. The ion beam is wide enough to impact an entire wafer surface as the support rotates each wafer through the ion beam.
Medium current implanters treat one wafer at a time. The wafers are supported in a cassette and are withdrawn one at time and placed on a platen. The wafer is then oriented in an implantation orientation so that the ion beam strikes the single wafer. These medium current implanters use beam shaping electronics to deflect a relatively narrow beam from its initial trajectory to selectively dope or treat the entire wafer surface.
Ion sources that generate the ion beams used in the known implanters typically include heated filament cathodes that tend to degrade with use. After relatively short periods of use, the filament cathodes must be replaced so that ions can again be generated with sufficient efficiency. Maximizing the interval between filament cathode replacement increases the amount of time wafers are being implanted and, thus, increases the efficiency of the implanter.